Definitions of mild cognitive impairment (MCI) vary, yielding conflicting results. For example, case definitions affect prevalence but not outcomes in prevalent cases. Our objective was to determine whether variation in case definitions affects outcomes in incident cases of MCI. The 5 year risks of death, institutionalisation, and dementia were evaluated in clinically examined incident MCI cases in the Canadian Study of Health and Aging. The definition of MCI was varied so as to include or relax combinations of diagnostic features from consensus criteria. Relative risks (RR) of each adverse outcome were highest in MCI case definitions that required subjective memory complaints (for example, RR of dementia = 26.4–38.7). Although each MCI definition conferred an increased risk of dementia, for each case definition 20–30% of survivors had no cognitive impairment at follow up. In this population based study, MCI represented a transitional state, but was heterogeneous, with substantial proportions recovering, regardless of how MCI was defined. Factors associated with recovery and non-progression in MCI require elucidation.
- CIND, cognitive impairment, no dementia
- CSHA, Canadian Study of Health and Aging
- IADL, instrumental activities of daily living
- MCI, mild cognitive impairment
- NCI, no cognitive impairment
- RR, relative risks
- mild cognitive impairment
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The CSHA was funded by the Seniors’ Independence Research Program, National Health Research and Development Program of Health Canada (project no. 6606-3954-MC(S)). These analyses were supported by the Canadian Institutes for Health Research (CIHR) (grant # MOP-62823). Kenneth Rockwood is supported by a CIHR Investigator Award and the Dalhousie Medical Research Foundation as the Kathryn Allen Weldon Professor of Alzheimer Research.
Competing interests: none declared
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